WO2021073097A1

WO2021073097A1 - Grounding detection method and device using same

Info

Publication number: WO2021073097A1
Application number: PCT/CN2020/092061
Authority: WO
Inventors: 陈鹏; 伍永富; 徐清清
Original assignee: 阳光电源股份有限公司
Priority date: 2019-10-16
Filing date: 2020-05-25
Publication date: 2021-04-22
Also published as: EP3992651A4; EP3992651A1; JP7223884B2; AU2020366408A1; CN110687476A; JP2022537689A; CN110687476B

Abstract

Provided are a grounding detection method and a device using same. The grounding detection method is applied to a controller in a PWM-control-type grid-connected inverter in a low-voltage power grid system, and comprises: when a PWM-control-type grid-connected inverter satisfies a grounding detection condition, first controlling a grounding power supply in the PWM-control-type grid-connected inverter to apply a preset current or a preset voltage between a preset position and the ground (S200), wherein the preset position is a pole of a direct-current bus in the PWM-control-type grid-connected inverter or an output end of an alternating-current-side coupling circuit; and then determining whether the voltage of a pole of the direct-current bus or the output end of the alternating-current-side coupling circuit with respect to the ground changes (S300), so as to determine whether the PWM-control-type grid-connected inverter is sufficiently grounded, thus realizing automatic detection of a grounding condition of the grid-connected inverter, thereby solving the problem in the prior art of the dependence on manual work.

Description

A grounding detection method and its application equipment

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on October 16, 2019, the application number is 201910983849.8, and the invention title is "a grounding detection method and its application equipment", the entire content of which is incorporated herein by reference Applying.

Technical field

The present invention relates to the field of power electronics technology, in particular to a grounding detection method and its application equipment.

Background technique

At present, according to safety regulations, when the grid-connected inverter realizes a reliable connection between its own grounding point and an external grounding point, it needs to ensure that its leakage current does not exceed the safety current of the human body. If the leakage current is large, it needs to be connected to the grid. The device has at least 2 grounding points to ensure reliable grounding.

However, during the grid-connected construction process, due to human negligence, poor grounding of the grid-connected inverter may occur, such as missing grounding points, broken grounding wires, or suspended grounding points, so that workers are in contact with the grid-connected inverters. There is a risk of electric shock when the chassis is installed. In addition, after a long-term operation of the grid-connected inverter, it may also cause poor grounding due to the increase in the bottom line impedance. If it is not found in time, the staff may also be shocked when they touch the housing of the grid-connected inverter. risk.

In order to avoid electric shock when touching the grid-connected inverter case, in the prior art, workers usually use test equipment to test the ground impedance of the grid-connected inverter on site, but this detection method involves manual work. Dependence.

Summary of the invention

In view of this, the present invention provides a grounding detection method and its application equipment to realize automatic detection of the grounding condition of the grid-connected inverter.

To achieve the foregoing objective, the embodiments of the present invention provide the following technical solutions:

The first aspect of the present application provides a grounding detection method, which is applied to a controller in a PWM-controlled grid-connected inverter in a low-voltage power grid system. The grounding detection method includes:

Judging whether the PWM-controlled grid-connected inverter satisfies the grounding detection condition;

If the PWM-controlled grid-connected inverter satisfies the grounding detection condition, control the grounded power source in the PWM-controlled grid-connected inverter to a preset position in the PWM-controlled grid-connected inverter and the ground A preset current or a preset voltage is applied between; the preset position is one pole of the DC bus or the output end of the AC-side coupling circuit;

Judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit to the ground changes;

If the voltage changes, it is determined that the PWM control type grid-connected inverter is badly grounded;

If the voltage does not change, it is determined that the PWM control type grid-connected inverter is well grounded.

Optionally, judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit to the ground changes, includes:

Judging whether the voltage between the negative electrode of the DC bus and the ground gradually decreases and approaches zero potential;

or,

Judging whether the voltage between the positive pole of the DC bus bar and the ground gradually increases and approaches the DC bus voltage;

or,

It is determined whether the voltage between the output terminal of the AC side coupling circuit and the ground gradually increases and approaches a preset value.

Optionally, the grounding detection condition includes: receiving a grounding detection instruction, and/or reaching a preset detection time.

Optionally, if the preset position is a pole of the DC bus, the grounding detection condition further includes:

The PWM control type grid-connected inverter is in a grid-connected state.

Optionally, if the preset position is the output terminal of the AC-side coupling circuit, the grounding detection condition further includes:

The PWM control type grid-connected inverter is in a standby or grid-connected state.

The second aspect of the present application provides a controller for executing the grounding detection method provided in the first aspect of the present application.

Optionally, the controller is connected to an output terminal of a grounding detection switch button outside the device where it is located, and receives a grounding detection instruction output by the grounding detection switch button.

Optionally, a timing module is provided inside the controller for notifying the controller to perform grounding detection after the current time reaches a preset detection time.

The third aspect of the present application provides a PWM controlled grid-connected inverter suitable for low-voltage power grid systems, including: a main circuit, a grounded power supply, a detection module, an AC-side coupling circuit, and the controller provided in the second aspect of the present application; wherein :

The DC side of the main circuit is used to receive or output DC power, and the AC side of the main circuit is used to output or receive AC power;

The AC side of the AC coupling circuit is connected to the AC side of the main circuit;

The negative pole of the grounded power supply is connected to the internal grounding point of the PWM-controlled grid-connected inverter; the positive pole of the grounded power supply is connected to a preset position in the PWM-controlled grid-connected inverter;

The preset position is a pole of the DC bus in the main circuit, or the output terminal of the AC coupling circuit;

The command output terminal of the controller is connected to the control terminal of the grounded power supply; the receiving terminal of the controller is connected to the output terminal of the detection module to receive one pole of the DC bus detected by the detection module Or the voltage between the output terminal of the AC-side coupling circuit and the ground.

Optionally, the grounding power supply includes: a controllable DC voltage source and a current-limiting resistor; where:

The positive pole of the controllable DC voltage source is connected to the positive pole of the grounding power source, and the negative pole of the controllable DC voltage source is connected to the negative pole of the grounding power source;

The current-limiting resistor is arranged between the positive electrode of the controllable DC voltage source and the positive electrode of the grounding power source;

or,

The current-limiting resistor is arranged between the negative electrode of the controllable DC voltage source and the negative electrode of the grounding power source;

The control terminal of the controllable DC voltage source serves as the control terminal of the grounding power supply.

Optionally, the grounded power supply includes: a controllable direct current source; where:

The positive pole of the controllable direct current source is used as the positive pole of the grounding power source;

The negative electrode of the controllable DC voltage source is used as the negative electrode of the grounding power supply;

The control terminal of the controllable direct current source serves as the control terminal of the grounding power supply.

Optionally, the AC-side coupling circuit is a rectifier, the output terminal of the AC-side coupling circuit is the DC side positive or the DC side negative of the rectifier, and the AC side of the rectifier is connected to the AC side of the main circuit ；

or,

The AC-side coupling circuit is a Y-type circuit composed of impedance, the output end of the AC-side coupling circuit is the virtual N point of the Y-type circuit, and the other three ends of the Y-type circuit are connected to the main circuit. The AC side is connected.

Optionally, the main circuit includes: an inverter circuit, or, an inverter circuit and a plurality of boost circuits connected in parallel to the DC bus on the high voltage side.

The fourth aspect of the present application provides a low-voltage power grid system, including a transformer, at least one DC power supply, and the PWM controlled grid-connected inverter provided in the third aspect of the present application; wherein:

The DC side of the PWM-controlled grid-connected inverter is connected to the DC power supply;

The AC side of the PWM controlled grid-connected inverter is connected to the grid through the transformer;

The midpoint of the transformer is grounded.

It can be seen from the above technical solutions that this application provides a grounding detection method and its application equipment, wherein the grounding detection method provided by this application is applied to a controller in a PWM controlled grid-connected inverter in a low-voltage power grid system. Compared with the prior art, the controller of the PWM-controlled grid-connected inverter of the present application first controls the PWM-controlled grid-connected inverter when the PWM-controlled grid-connected inverter meets the grounding detection condition The neutral grounding power supply applies a preset current or a preset voltage between a preset position in the PWM control type grid-connected inverter and the ground, wherein the preset position is a pole of the DC bus or the output terminal of the AC-side coupling circuit; After that, by judging whether the voltage between one pole of the DC bus or the output end of the AC-side coupling circuit and the ground has changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, and then the grid-connected inverter is realized. The automatic detection of the grounding condition of the generator solves the problem of artificial dependence in the prior art.

Description of the drawings

FIG. 1 is a schematic flowchart of a grounding detection method provided by an embodiment of this application;

2 and 3 are schematic diagrams of two structures of the PWM control grid-connected inverter provided by the embodiments of the application;

FIG. 4 is a schematic structural diagram of a rectifier provided by an embodiment of the application;

FIG. 5 is a schematic structural diagram of a Y-type circuit provided by an embodiment of the application;

Fig. 6a is a schematic structural diagram of a TN-C system provided by an embodiment of this application;

FIG. 6b is a schematic structural diagram of a TN-C-S system provided by an embodiment of this application;

Fig. 6c is a schematic structural diagram of a TN-S system provided by an embodiment of the application;

Figure 6d is a schematic structural diagram of a TT system provided by an embodiment of the application.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

In this application, the terms "include", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes no Other elements clearly listed, or also include elements inherent to this process, method, article, or equipment. If there are no more restrictions, the element defined by the sentence "including a..." does not exclude the existence of other identical elements in the process, method, article, or equipment that includes the element.

In order to realize the automatic detection of the grounding condition of the grid-connected inverter, an embodiment of the present application provides a grounding detection method, which is applied to a controller in a PWM-controlled grid-connected inverter in a low-voltage power grid system.

Among them, the specific structure of the PWM controlled grid-connected inverter is shown in Figures 2 and 3, including: a main circuit 10, a grounded power supply 20, a detection module 30, a controller 40, and an AC-side coupling circuit 50 (not shown in Figure 2 show).

The DC side of the main circuit 10 is used for receiving or outputting DC power, and the AC side of the main circuit 10 is used for outputting or receiving AC power. The AC side of the AC side coupling circuit 50 is connected to the AC side of the main circuit 10.

The positive pole of the grounded power source 20 is connected to a preset position in the PWM control type grid-connected inverter; wherein, the preset position is: one pole of the DC bus (shown in Figure 2 with the negative pole as an example), or, the AC side The output terminal of the coupling circuit (the port on the left side of the AC side coupling circuit 50 in FIG. 3); the negative electrode of the grounding power supply 20 is connected to the internal grounding point of the PWM control type grid-connected inverter.

The command output terminal of the controller 40 is connected to the control terminal of the grounded power supply 20; the receiving terminal of the controller 40 is connected to the output terminal of the detection module 30, and receives one pole of the DC bus or the AC side coupling circuit 50 detected by the detection module 30 The voltage between the output terminal and the ground.

Specifically, the specific process of the grounding detection method is shown in Fig. 1, and includes the following steps:

S100: Determine whether the PWM control type grid-connected inverter meets the grounding detection condition.

Wherein, the grounding detection condition of the PWM-controlled grid-connected inverter is: receiving a grounding detection instruction, and/or reaching a preset detection time. In practical applications, the grounding detection command is generated by the staff after pressing the grounding detection button when the PWM control type grid-connected inverter needs to be grounded. It should be noted that after pressing the grounding detection button once, only A grounding detection command can be generated once; and the preset detection time can be at least one preset time point, or at least one preset time point with periodicity, which is not specifically limited here, depending on the specific situation However, they are all within the scope of protection of this application.

In practical applications, the PWM control grid-connected inverter can be grounded only when the grounding detection instruction is received and/or when the preset time is reached; if the PWM-controlled grid-connected inverter meets the grounding detection If the condition is met, step S200 is executed. If the PWM-controlled grid-connected inverter does not meet the grounding detection condition, then the PWM-controlled grid-connected inverter will not be grounded.

In practical applications, when the preset position is one pole of the DC bus, the grounding detection condition also includes: the PWM-controlled grid-connected inverter is in a grid-connected state.

Among them, the grid-connected state of the PWM-controlled grid-connected inverter refers to the position of the PWM-controlled grid-connected inverter when all the switches in the main circuit 10 of the PWM-controlled grid-connected inverter are closed. status.

It should be noted that when the preset position is one pole of the DC bus, if the PWM-controlled grid-connected inverter is in the grid-connected state, and the controller 40 of the PWM-controlled grid-connected inverter receives the grounding detection Command, the PWM-controlled grid-connected inverter meets the grounding detection conditions; or, if the PWM-controlled grid-connected inverter is in the grid-connected state and the current time reaches the preset detection time, the PWM-controlled grid-connected inverter The inverter meets the grounding detection conditions.

In practical applications, when the preset position is the output terminal of the AC-side coupling circuit 50, the grounding detection condition also includes: the PWM-controlled grid-connected inverter is in a standby state, or a grid-connected state.

Among them, the standby state of the PWM-controlled grid-connected inverter refers to: when all the switches in the main circuit 10 of the PWM-controlled grid-connected inverter are turned off, the PWM-controlled grid-connected inverter is located status. It can be seen that the standby state is the state before grid connection.

It should be noted that when the preset position is the output terminal of the AC-side coupling circuit 50, if the PWM-controlled grid-connected inverter is in the standby state or grid-connected state, and the control of the PWM-controlled grid-connected inverter If the inverter 40 receives the grounding detection instruction, the PWM-controlled grid-connected inverter meets the grounding detection conditions; or, if the PWM-controlled grid-connected inverter is in the standby state or grid-connected state, and the current time reaches the preset detection Time, the PWM-controlled grid-connected inverter meets the grounding detection conditions.

S200. Control the grounded power supply in the PWM-controlled grid-connected inverter to apply a preset current or a preset voltage between a preset position in the PWM-controlled grid-connected inverter and the ground.

Among them, the preset current is a preset input current, and the preset voltage is a preset input voltage; in practical applications, the preset current or the preset voltage needs to be reasonably selected according to actual conditions.

The preset position in FIG. 2 is the negative pole of the DC bus, and the case where the positive pole of the DC bus is the preset position is not shown; the preset position in FIG. 3 is the output terminal of the AC-side coupling circuit 50. In practical applications, The AC side coupling circuit 50 may be the rectifier shown in FIG. 4, or a Y-shaped circuit composed of impedance shown in FIG. 5; when the AC side coupling circuit 50 is a rectifier, the AC side of the rectifier and the AC side of the main circuit 10 The output terminal of the AC-side coupling circuit 50 refers to the DC-side positive or DC-side negative of the rectifier; when the AC-side coupling circuit 50 is a Y-shaped circuit composed of impedance, the other three ends of the Y-shaped circuit are connected to the main circuit 10 The AC side is connected, and the output terminal of the AC side coupling circuit 50 refers to the virtual N point of the Y-shaped circuit.

S300: Determine whether the voltage between one pole of the DC bus or the output end of the AC-side coupling circuit to the ground has changed.

In practical applications, if the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground changes, it means that the applied preset current or preset voltage cannot be completely directed to the ground, and step S400 is executed. If the voltage between one pole of the DC bus or the output terminal of the AC side coupling circuit 50 to the ground does not change, it means that the applied preset current or preset voltage is completely directed to the ground, and step S500 is performed.

Specifically, whether the preset position is one pole of the DC bus or the output terminal of the AC-side coupling circuit 50, it can be determined whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground is Change to determine whether the PWM control type grid-connected inverter is badly grounded. Moreover, in practical applications, the specific implementation for judging whether the voltage between the negative electrode of the DC bus bar and the ground has changed is: judging whether the voltage between the negative electrode of the DC bus bar and the ground is gradually decreasing and approaching zero potential; and judging The specific implementation of whether the voltage between the positive pole of the DC bus bar and the ground changes is: judging whether the voltage between the positive pole of the DC bus bar and the ground gradually increases and approaches the DC bus voltage; at this time, if the negative pole of the DC bus bar is The voltage between the ground gradually decreases and approaches zero potential, or the voltage between the positive pole of the DC bus and the ground gradually increases and approaches the DC bus voltage, then step S400 is performed; at this time, if the negative pole of the DC bus is The voltage between the ground remains unchanged, or the voltage between the positive pole of the DC bus and the ground remains unchanged, then step S500 is executed.

When the AC-side coupling circuit 50 is specifically a Y-shaped circuit, the specific implementation for judging whether the voltage between the output terminal of the AC-side coupling circuit 50 and the ground has changed is: judging whether the virtual N point of the Y-shaped circuit is between the virtual point and the ground. Whether the voltage gradually rises and approaches the preset value, at this time, if the voltage between the virtual point N of the Y-type circuit and the ground gradually rises and approaches the preset value, step S400 is executed; at this time, if the Y-type circuit The voltage between the virtual point N of the circuit and the ground remains unchanged, and step S500 is executed. The preset value refers to a specific value of the preset current or preset voltage applied by the controller 40 to control the grounding power source 20.

It should be noted that if the preset position is one pole of the DC bus, after grid connection, the controller 40 can detect the voltage conversion between one pole of the DC bus and the ground to achieve grounding detection, or it can detect AC The side coupling circuit 50 converts the voltage between the ground to realize grounding detection. When the preset position is the output end of the AC-side coupling circuit 50, the grounded power supply 20 can be controlled to apply a preset current or a preset voltage to the output end of the AC-side coupling circuit 50 before grid connection, and the DC bus is in the main circuit 10 Under the reverse conversion action of the inverter circuit, it realizes its own soft start and establishes a normal DC bus voltage. Therefore, after applying a preset current or a preset voltage to the output terminal of the AC-side coupling circuit 50, if the PWM control type is parallel When a ground fault occurs in the grid inverter, not only can the voltage change be detected at the output end of the AC-side coupling circuit 50, but also the voltage change can be measured at one pole of the DC bus.

Moreover, when the preset position is the output terminal of the AC-side coupling circuit 50, it is determined whether the PWM control type grid-connected inverter is badly grounded by judging whether the voltage between the output terminal of the AC-side coupling circuit 50 and the ground changes. Therefore, related operations on the main circuit 10 of the inverter circuit can be avoided, and the detection steps can be simplified.

S400: Determine that the PWM control type grid-connected inverter is badly grounded.

S500: Determine that the PWM control type grid-connected inverter is well grounded.

It should be noted that step S100 in this embodiment can be executed according to its own cycle, and step S200, step S300, step S400, and step S500 are executed according to the above logic trigger, that is, only after step S100 is executed, Step S200, step S300, step S400 and step S500 will be executed accordingly; moreover, as a whole, in the whole detection process, every other cycle, it is judged whether to ground the PWM control type grid-connected inverter. Detection, when the period takes a minimum value, it can be continuously judged whether to perform grounding detection on the PWM-controlled grid-connected inverter, so that the PWM-controlled grid-connected inverter can be grounded in time.

Alternatively, step S100, step S200, step S300, step S400, and step S500 can also be executed according to the above logic cycle trigger, that is, when the whole detection process completes step S400 or step S500, return to trigger execution step S100, so that step S100, Step S200, step S300, step S400, and step S500 form a loop; when the loop is formed, it can continuously determine whether the PWM control type grid-connected inverter is grounded or not, so that the PWM control type parallel inverter can be detected in time. The grid inverter performs grounding detection; however, it should be noted that when the controller 40 is turned on, the entire detection process starts.

It can be seen from the above technical solution that the controller 40 of the PWM-controlled grid-connected inverter first controls the grounding in the PWM-controlled grid-connected inverter when the PWM-controlled grid-connected inverter meets the grounding detection conditions. The power supply 20 applies a preset current or a preset voltage between a preset position in the PWM-controlled grid-connected inverter and the ground, where the preset position is a pole of the DC bus or the output terminal of the AC-side coupling circuit 50; After that, by judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground has changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, thereby realizing the inverse of the grid-connected inverter. The automatic detection of the grounding condition of the transformer solves the problem of artificial dependence in the prior art.

It is worth noting that the grounding detection method provided in this embodiment only needs to apply a predetermined current or a predetermined voltage between the predetermined position of the PWM-controlled grid-connected inverter and the ground before and after the grounding power supply 20 applies a predetermined current or a predetermined voltage. If the voltage between the output terminal of the AC-side coupling circuit 50 and the ground is changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, so that the grounding detection method provided by this embodiment is simple, Convenient and reliable.

Another embodiment of the present application provides a controller for executing the grounding detection method shown in FIG. 1.

In practical applications, the controller is connected to the output terminal of the grounding detection switch button outside the device where it is located, and receives the grounding detection command output by the grounding detection switch button. It should be noted that the condition for the grounding detection switch button to generate the grounding detection instruction is: when the PWM control type grid-connected inverter needs to be grounded, the worker presses the grounding detection switch button.

In addition, in practical applications, a timing module is provided inside the controller, and the timing module is used to notify the controller to perform grounding detection after the current time reaches the preset detection time.

Another embodiment of the present application provides a PWM controlled grid-connected inverter suitable for low-voltage power grid systems. The specific structure is shown in Figures 2 and 3, including: a main circuit 10, a grounded power supply 20, and a detection module 30 , AC side coupling circuit 50 (not shown in FIG. 2) and the controller 40 provided in the previous embodiment.

Among them, the DC side of the main circuit 10 is used to receive or output DC power, and the AC side of the main circuit 10 is used to output or receive AC power. The AC side of the AC side coupling circuit 50 is connected to the AC side of the main circuit 10.

The negative pole of the grounding power source 20 is connected to the internal grounding point of the PWM-controlled grid-connected inverter; the positive pole of the grounding power source 20 is connected to the preset position in the PWM-controlled grid-connected inverter.

The command output terminal of the controller 40 is connected to the control terminal of the grounded power source 20; the receiving terminal of the controller 40 is connected to the output terminal of the detection module 30, and receives one pole of the DC bus detected by the detection module 30, that is, the positive or negative pole of the DC bus. The negative pole (as shown in FIG. 2), or the voltage between the output terminal of the AC side coupling circuit 50 (as shown in FIG. 3) and the ground.

It should be noted that if the AC side coupling circuit 50 is not used to realize the grounding detection function, the preset position is one pole of the DC bus. Figure 2 shows the negative pole of the DC bus as an example. At this time, the controller 40 receives The voltage received by the terminal through the detection module 30 can be the voltage between the negative pole of the DC bus and the ground, or the voltage between the positive pole of the DC bus and the ground. There is no specific limitation here, and it depends on the specific situation. All are within the protection scope of this application.

If the AC-side coupling circuit 50 is used to implement the grounding detection function, when the preset position is the output end of the AC-side coupling circuit 50, the receiving end of the controller 40 receives the voltage detected by the detection module 30, which can be a pole of the DC bus. The voltage between the ground (not shown) can also be the voltage between the output terminal of the AC-side coupling circuit 50 and the ground (as shown in FIG. 3), which is not specifically limited here, and can be changed according to specific circumstances. Are all within the scope of protection of this application. In addition, the AC side coupling circuit 50 is used to implement the grounding detection function. The preset position can also be a pole of the DC bus. At this time, the receiving end of the controller 40 receives the voltage detected by the detection module 30, which is the AC side coupling circuit 50. The voltage between the output terminal and the earth.

In practical applications, the AC-side coupling circuit 50 may be a rectifier. The specific structure of the rectifier is shown in FIG. 4, including: a capacitor C and three rectifying branches 60; the rectifying branch 60 is composed of two diodes D in series.

Among them, the positive poles of the three rectifying branches 60 are connected to one end of the capacitor C, and the connection point is used as the positive pole of the rectifier DC side; the positive poles of the three rectifying branches 60 are connected to the other end of the capacitor C, and the connection point is used as the negative pole of the rectifier DC side. The output end of the AC-side coupling circuit 50 refers to the positive or negative pole of the DC side; the intermediate connection points of the three rectifying branches 60 are used as the AC side of the rectifier, which are connected to the connection points of each phase of the AC side of the main circuit 10 respectively.

In practical applications, the AC-side coupling circuit 50 may also be a Y-type circuit composed of impedances. The specific structure of the Y-type circuit is shown in FIG. 5, including: a first impedance Z1, a second impedance Z2, and a third impedance Z3.

Among them, one end of the first impedance Z1, one end of the second impedance Z2, and one end of the third impedance Z3 are all connected, and the connection point is used as the virtual point N of the Y-type circuit; the output end of the AC-side coupling circuit 50 refers to the Y-type circuit Virtual point N; the other end of the first impedance Z1, the other end of the second impedance Z2, and the other end of the third impedance Z3 are all connected to the AC side of the main circuit 10.

It should be noted that the first impedance Z1, the second impedance Z2, and the third impedance Z3 can all be pure resistance, pure capacitance, or pure inductance, or all of them can be a combination of at least any two of resistance, capacitance, and inductance. There is no specific limitation, and combinations can be made according to specific circumstances, and all are within the protection scope of this application.

For the grounding detection method executed by the controller 40, refer to the above-mentioned embodiment, which will not be repeated here. It is worth noting that for the PWM controlled grid-connected inverter shown in FIG. 2 and the preset position is one pole of the DC bus and the detection module 30 detects the voltage between the output terminal of the AC side coupling circuit 50 and the ground , The controller 40 can only perform grounding detection after grid connection; while the PWM control type grid-connected inverter shown in FIG. 3, and the preset position is the output terminal of the AC-side coupling circuit 50, and the detection module 30 detects the DC bus When the voltage is between the negative pole of the power and the ground, the controller 40 can not only perform grounding detection after grid connection, but also perform grounding detection before grid connection. In particular, if the structure of the AC-side coupling circuit 50 is as shown in FIG. 5, and the predetermined position where the grounding power source 20 in the PWM-controlled grid-connected inverter applies a preset voltage or a preset current is the AC-side coupling circuit At the same time, the voltage detected by the detection module 30 is the voltage between the output terminal of the AC-side coupling circuit 50 and the ground, so it can not only perform grounding detection before grid connection, but also avoid damage to the main circuit 10 Perform related operations.

Another embodiment of the present application provides a specific implementation of the grounded power supply 20. The specific structure is shown in FIG. 2 or FIG. 3, and includes: a controllable DC voltage source 21 and a current-limiting resistor R.

Among them, the positive pole of the controllable DC voltage source 21 is connected to the positive pole of the grounding power source 20; the negative pole of the controllable DC voltage source 21 is connected to the negative pole of the grounding power source 20, and the control terminal of the controllable DC voltage source 21 is used as the control terminal of the grounding power source 20; The current resistance R is arranged between the positive electrode of the controllable DC voltage source 21 and the positive electrode of the grounding power source 20, or the current limiting resistor R is arranged between the negative electrode of the controllable DC voltage source 21 and the negative electrode of the grounding power source 20.

It should be noted that the current-limiting resistor R can effectively limit the output capability of the controllable DC voltage source 21 to avoid electric shocks to workers.

The foregoing only shows a preferred embodiment of the grounded power source 20. In practical applications, the grounded power source 20 may also include a controllable direct current source; wherein, the positive electrode of the controllable direct current source serves as the positive electrode of the grounded power source 20, and the controllable direct current source The negative pole of the current source serves as the negative pole of the grounded power supply 20, and the control terminal of the controllable DC current source serves as the control terminal of the grounded power supply 20. It should be noted that the two implementations of the grounding power supply 20 may be determined according to specific conditions, and both are within the protection scope of the present application.

This embodiment also provides two implementations of the main circuit 10, the first specific implementation includes: an inverter circuit 11; the second implementation includes: an inverter circuit 11 and multiple boosters connected in parallel with the high-voltage side of the DC bus Circuit 12 (as shown in Fig. 2 and Fig. 3); it should be noted that the two implementation manners may be determined according to specific circumstances, and both are within the protection scope of the present application.

It should be noted that the controller 40 provided in this embodiment borrows the existing circuit inside the PWM-controlled grid-connected inverter in the low-voltage power grid system without adding new circuits or external tools. The grounding detection of the PWM-controlled grid-connected inverter reduces its own cost, which is convenient for market promotion and competition.

Another embodiment of the present application provides a low-voltage power grid system, the specific structure of which is shown in FIGS. 6a-6d, including: a transformer (a part of the transformer is shown as a black square in FIGS. 6a-6d), and at least one DC The power supply 80 and the PWM control type grid-connected inverter 90 shown in FIG. 2 or FIG. 3.

The DC side of the PWM-controlled grid-connected inverter 90 is connected to a DC power supply 80; the AC side of the PWM-controlled grid-connected inverter 90 is connected to the grid through a transformer; the midpoint of the transformer is grounded.

Optionally, the DC power supply 80 can be a photovoltaic string, an energy storage system, or a photovoltaic string and an energy storage system. There is no specific limitation here, and it depends on the specific circumstances, all of which are protected in this application. Within range.

In practical applications, if the PE line of the PWM control grid-connected inverter 90 is connected to the PEN line of the transformer, and the PEN line of the transformer is connected to the neutral point of the transformer, the PWM control type grid-connected with the above-mentioned connection method is adopted The inverter 90 and the transformer form a TN-C system (as shown in Fig. 6a).

In practical applications, if the PE wire of the PWM controlled grid-connected inverter 90 is connected to the PE wire of the transformer, the PE wire of the transformer is connected to the N wire of the transformer, and the connection point of the PE wire of the transformer and the N wire of the transformer is connected to the transformer If the center points of the two are connected, the PWM-controlled grid-connected inverter 90 and the transformer in the above-mentioned connection mode form a TN-CS system (as shown in Fig. 6b).

In practical applications, if the PE line of the PWM-controlled grid-connected inverter 90 is connected to the PE line of the transformer, and the N line and PE line of the transformer are both connected to the center point of the transformer, the PWM of the above-mentioned connection mode is adopted. The controlled grid-connected inverter 90 and the transformer form a TN-S system (as shown in Figure 6c).

In practical applications, if the PE line of the PWM-controlled grid-connected inverter 90 is grounded and the N line of the transformer is connected to the neutral point of the transformer, the PWM-controlled grid-connected inverter 90 and the neutral point of the transformer are connected by the above-mentioned connection method. The transformer forms the TT system (as shown in Figure 6d).

The above-mentioned four connection forms of the PWM-controlled grid-connected inverter 90 and the transformer may be determined according to specific conditions, and are not specifically limited here, and they are all within the protection scope of the present application.

The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for related parts, please refer to the part of the description of the method embodiment. The system and system embodiments described above are merely illustrative, where the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, It can be located in one place, or it can be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the objectives of the solutions of the embodiments. Those of ordinary skill in the art can understand and implement it without creative work.

Professionals may further realize that the units and algorithm steps of the examples described in the embodiments disclosed in this article can be implemented by electronic hardware, computer software, or a combination of the two, in order to clearly illustrate the possibilities of hardware and software. Interchangeability, in the above description, the composition and steps of each example have been generally described in accordance with the function. Whether these functions are executed by hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods for each specific application to implement the described functions, but such implementation should not be considered as going beyond the scope of the present invention.

The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown in this document, but should conform to the widest scope consistent with the principles and novel features disclosed in this document.

Claims

A grounding detection method, characterized in that it is applied to a controller in a PWM-controlled grid-connected inverter in a low-voltage power grid system. The grounding detection method includes:

Judging whether the PWM-controlled grid-connected inverter satisfies the grounding detection condition;

If the PWM-controlled grid-connected inverter satisfies the grounding detection condition, the grounded power supply in the PWM-controlled grid-connected inverter is controlled to transfer to the preset position and ground in the PWM-controlled grid-connected inverter. A preset current or a preset voltage is applied between; the preset position is one pole of the DC bus or the output end of the AC-side coupling circuit;

Judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit to the ground changes;

If the voltage changes, it is determined that the PWM control type grid-connected inverter is badly grounded;

If the voltage does not change, it is determined that the PWM control type grid-connected inverter is well grounded.
The grounding detection method according to claim 1, wherein determining whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit and the ground has changed comprises:

Judging whether the voltage between the negative electrode of the DC bus and the ground gradually decreases and approaches zero potential;

Or, judging whether the voltage between the positive pole of the DC bus bar and the ground gradually increases and approaches the DC bus voltage;

Alternatively, it is determined whether the voltage between the output terminal of the AC-side coupling circuit and the ground gradually increases and approaches a preset value.
The grounding detection method according to claim 1, wherein the grounding detection condition comprises: receiving a grounding detection instruction, and/or reaching a preset detection time.
The grounding detection method according to claim 3, wherein if the preset position is a pole of a DC bus, the grounding detection condition further comprises:

The PWM control type grid-connected inverter is in a grid-connected state.
The grounding detection method according to claim 3, wherein if the preset position is the output terminal of the AC-side coupling circuit, the grounding detection condition further comprises:

The PWM control type grid-connected inverter is in a standby or grid-connected state.
A controller, characterized in that it is used to implement the grounding detection method according to any one of claims 1-5.
The controller according to claim 6, wherein the controller is connected to an output terminal of a grounding detection switch button outside the device where it is located, and receives a grounding detection instruction output by the grounding detection switch button.
The controller according to claim 6, wherein a timing module is provided inside the controller for notifying the controller to perform grounding detection after the current time reaches the preset detection time.
A PWM-controlled grid-connected inverter, characterized in that it is suitable for low-voltage power grid systems, and includes: a main circuit, a grounded power supply, a detection module, an AC-side coupling circuit, and the control according to any one of claims 6-8器; where:

The DC side of the main circuit is used to receive or output DC power, and the AC side of the main circuit is used to output or receive AC power;

The AC side of the AC coupling circuit is connected to the AC side of the main circuit;

The negative pole of the grounded power supply is connected to the internal grounding point of the PWM-controlled grid-connected inverter; the positive pole of the grounded power supply is connected to a preset position in the PWM-controlled grid-connected inverter;

The preset position is a pole of the DC bus in the main circuit, or the output terminal of the AC coupling circuit;

The command output terminal of the controller is connected to the control terminal of the grounded power supply; the receiving terminal of the controller is connected to the output terminal of the detection module to receive one pole of the DC bus detected by the detection module Or the voltage between the output terminal of the AC-side coupling circuit and the ground.
The PWM controlled grid-connected inverter according to claim 9, wherein the grounded power supply includes: a controllable DC voltage source and a current limiting resistor; wherein:

The positive pole of the controllable DC voltage source is connected to the positive pole of the grounding power source, and the negative pole of the controllable DC voltage source is connected to the negative pole of the grounding power source;

The current-limiting resistor is arranged between the positive pole of the controllable DC voltage source and the positive pole of the grounding power source, or between the negative pole of the controllable DC voltage source and the negative pole of the grounding power source;

The control terminal of the controllable DC voltage source serves as the control terminal of the grounding power supply.
The PWM controlled grid-connected inverter according to claim 9, wherein the grounded power supply comprises: a controllable direct current source; wherein:

The positive pole of the controllable direct current source is used as the positive pole of the grounding power source;

The negative electrode of the controllable DC voltage source is used as the negative electrode of the grounding power supply;

The control terminal of the controllable direct current source serves as the control terminal of the grounding power supply.
The PWM controlled grid-connected inverter according to claim 9, wherein the AC-side coupling circuit is a rectifier, and the output terminal of the AC-side coupling circuit is the DC-side anode or the DC-side cathode of the rectifier , The AC side of the rectifier is connected to the AC side of the main circuit;

or,

The AC-side coupling circuit is a Y-type circuit composed of impedance, the output end of the AC-side coupling circuit is the virtual N point of the Y-type circuit, and the other three ends of the Y-type circuit are connected to the main circuit. The AC side is connected.
The PWM controlled grid-connected inverter according to claim 9, wherein the main circuit comprises: an inverter circuit, or, the inverter circuit and a plurality of boost circuits connected in parallel with the high-voltage side of the DC bus.
A low-voltage power grid system, characterized by comprising a transformer, at least one DC power supply, and the PWM controlled grid-connected inverter according to any one of claims 9-13; wherein:

The DC side of the PWM-controlled grid-connected inverter is connected to the DC power supply;

The AC side of the PWM controlled grid-connected inverter is connected to the grid through the transformer;

The midpoint of the transformer is grounded.